A fuel tank having an outer metal shell and an inner liner of elastomeric material is known and disclosed in U.S. Pat. No. 4,625,980 to Lyzohub. Also, a fuel tank with a resilient diaphragm or bladder is known and disclosed in U.S. Pat. No. 3,477,610 to Hansen and in U.S. Pat. No. 3,887,104 to Cole. The Lyzohub patent does not provide for a resilient bladder or diaphragm to separate liquid fuel from the remainder of the space in the fuel tank. In a typical fuel tank used in automobiles, the remainder of the fuel tank may be referred to as the "air space" although the space is actually filled with a mixture of air and fuel vapor. In filling a fuel tank of this type, the fuel vapor is pushed out of the tank by the new liquid fuel. This vapor will enter the atmosphere unless some means is provided to capture the vapor. Such a capture means represents a costly way to prevent the escape of the vapor.
The above identified Hansen patent discloses a fuel storage tank such as would be buried underground at a gas station. The tank interior includes a liner or resilient material overlying inner walls of an outer housing. The liner is attached to the fill opening of the tank so that fuel is introduced in the space defined by the liner. As liquid fuel leaves the tank, the liner separates from the outer walls of the tank and follows the decreasing liquid fuel level. The space between the liner and the outer housing increases in volume as fuel leaves the tank thus defining a true air space in that the space does not contain air and fuel vapor. Such an arrangement does not produce the above described discharge of vapor from the tank.
The previously identified Cole patent also discloses a lined fuel tank with bladder means to separate liquid and vaporous fuel from an air space. In Cole, the fill tube and outlet tube are located at one end of the tank interior. This arrangement requires only that portion of the liner adjacent the tubes to maintain contact with the tank wall and frees the remaining portion of the liner to separate from the tank wall as the liquid fuel level decreases. The space between the liner and the outer tank wall thus defines an air space.